Axial force sensor

Abstract

A low-cost, compact, high-precision axial force sensor is provided. The axial force sensor includes a pair of parallel pressing plates and a strain gauge sandwiched therebetween. The strain gauge includes a plurality of strain-sensitive resistive elements around its periphery, and is provided with a spacer that transmits a pressing force from the pressing plates to some of the strain-sensitive elements but blocks the pressing force to the rest of the strain-sensitive elements. The output signal of the strain-sensitive elements blocked from the pressing force provide an accurate baseline to compare the output signal of the strain-elements subjected to the pressing force. The spacer has a uniform pattern of open and closed portions. On the strain gauge, the strain-sensitive elements are provided at both the open and closed portions of the spacer.

The invention claimed is: 
     
       1. An axial force sensor, comprising:
 a pair of pressing plates; 
 a strain gauge arranged in parallel with, and sandwhiched between, the pair of pressing plates, the strain gauge having a plurality of strain-sensitive elements including resistors, and 
 a transmitting and blocking mechanism that transmits a pressing force from the pair of pressing plates to at least one of the plurality of strain-sensitive elements and blocks the pressing force from the rest of the strain-sensitive elements, 
 wherein the transmitting and blocking mechanism is a plate-like spacer arranged between the pair of pressing plates together with the strain gauge, the plate-like spacer having at least one open, force-blocking portion and at least one closed, force-transmitting portion; and 
 wherein one or more strain-sensitive elements of the strain gauge are respectively aligned with the at least one open, force-blocking portion and the at least one closed, force-transmitting portion. 
 
     
     
       2. The axial force sensor according to  claim 1 ,
 wherein the spacer is formed in a ring shape, and has a plurality of alternating open, force-blocking portions and closed, force-transmitting portions arranged at constant angular intervals in a circumferential direction, and 
 wherein the plurality of strain-sensitive elements of the strain gauge are arranged at constant angular intervals at positions corresponding to the open, force-blocking portions and positions of the closed, force-transmitting of the ring shaped spacer. 
 
     
     
       3. The axial force sensor according to  claim 1 , further comprising a Wheatstone bridge circuit wherein the strain-sensitive elements to which the pressing force is transmitted are arranged on opposite sides to each other and wherein the strain-sensitive elements to which the pressing force is blocked are arranged on opposite sides to each other.